Ubuntu – Where I can find a summary of Ubuntu’s current functionality on touch screen devices

Yes, it can! According to my experience, Ubuntu 16.04 works perfectly with touch screen and 2 in 1 devices. I have Lenovo X230 Tablet and all of its features, including the Wacom stylus (and 3G module), work better under Ubuntu than under Windows. That is strange because the device is 'designed' for Windows.

Something more, within Ubuntu I was able to solve some little issues that I couldn't solve within Windows, for example: How do I disable the touchpad when the lid is twisted or closed?

Here is a demo how my stylus works with Gimp: GIMP Pressure sensitivity. Note that, I have not installed any additional (software) drivers to got the touch features to work.